The present invention relates generally to communication networks, and more specifically, to a scalable optical switch that uses substrates to demultiplex and multiplex input and output signals for optical networks.
Wave Division Multiplexing (WDM) is an optical networking technology that offers enormous bandwidth capabilities. With WDM, data is transmitted through optical fibers using wavelengths or lambdas. By transmitting lambda signals each of a different wavelength channel, multiple data streams can be simultaneously transmitted through a single fiber. Bandwidth is further increased by bundling multiple fibers together. The potential bandwidth for WDM systems in the future is virtually limitless as advances in the number of wavelength channels per fiber and the number of fibers that can be bundled together are made.
Wavelength routing is one challenge currently confronting designers developing WDM networking systems. Ideally designers would like to route optical signals of different wavelengths entirely in the optical domain. This would eliminate the need to convert optical signals into electrical signals and vice-versa. Wavelength routing involves the ability to switch optical signals from one fiber to another. Currently photonic cross-connect systems or re-configurable optical switches that perform this function are known. One known technology uses two-dimensional arrays of Micro Electro-Mechanical System (MEMS) mirrors in a three-dimensional configuration to switch optical signals from any input fiber to any output fiber. Since photonic cross-connects only perform optical switching, demultiplexers are needed to separate individual wavelengths from the fibers prior to switching and multiplexers are needed to place the switched wavelengths signals onto output fibers. For M fibers with N channels an Mxc3x97N-by-Mxc3x97N switch with (NM)2 possible connections is needed. Because one wavelength entering the switching matrix is only to be switched to an output port of same wavelength, only Nxc3x97M2 connections are actually needed. The complexity can be reduced to the minimum number of connections by using N M-by-M switches. However it still requires two Nxc3x97M fiber interconnections between the de/multiplexers and the switching matrix. To eliminate the fiber interconnections, which is a bottleneck for large number of fibers and channels, and to potentially increase the performance of the system, the integration of the de/multiplexing function with the switching matrix is needed.
One known way of integrating the de/multiplexing capability is to use dispersive elements such as reflection gratings with MEMS mirrors. See for example U.S. Pat. Nos. 5,960,133 and 6,097,859, both incorporated herein for all purposes. With these types of devices, a first grating is typically used to separate (demultiplex) the channels on the input fibers into individual wavelength signals or lambdas. The MEMS array is then used to switch the wavelength (lambda) signals to a second grating, which is configured in the opposite direction of the first grating. The second grating multiplexes the wavelength signals onto the output fibers.
Gratings used to disperse optical beams in free-space into different wavelength components are problematic for several reasons. They are difficult to align with other optical components in the switch. They also increase the optical path between the inputs and outputs of the switch, thereby increasing signal attenuation, which reduces the performance of the switch. Finally, they are polarization dependent, meaning the amount of signal attenuation through the gratings is highly dependent on the polarization of the incoming signals. Accordingly the use of gratings significantly complicates the design of current optical switches, reduces performance, and limits the scalability of these devices.
A scalable optical switch that uses stackable substrates to demultiplex and multiplex input and output signals for optical networks is therefore needed.
The present invention relates to a scalable optical switch that uses substrates to demultiplex and multiplex input and output signals for optical networks. The switch includes a plurality of input fibers each configured to carry a plurality of lambda signals, a first stack of substrates, each of the substrates coupled to one of the input fibers and configured to demultiplex the lambda signals received on the input fiber by wavelength respectively, a plurality of output fibers, and a switching matrix configured to switch the demultiplexed lambda signals from the first stack of substrates to the plurality of output fibers. In one embodiment, the switch further includes a second stack of substrates coupled between the switching matrix and the output fibers. Each of the substrates of the second stack is configured to multiplex the switched lambda signals onto one of the output fibers respectively. In an alternative embodiment, the second stack of substrates is replaced with a fixed mirror so that the input fibers can also be used as output fibers. In other embodiments of the invention, alignment plates are used to align the substrates of the first stack and/or the second stack respectively. In yet other embodiments, the optical switch of the present invention is scalable to form a large photonic switching system where individual switches are each used for specific bands or sub-bands of amplification.